It is well known in conventional printers, such for example as dot matrix printers, to provide the user with the ability to readily adjust the spacing between the print head and the platen which operatively supports the paper or other material on which printing is to occur. This adjustment enables paper or forms or the like of a relatively wide range of thicknesses to be accomodated by the printer. There is also, however, a "base setting" which corresponds to the minimum permissable distance or spacing between the print head and platen and beyond which the user may not normally adjust the print head-to-platen spacing. For example, a dot-matrix wire print head may have an operating stroke of the printing wires of about 0.2 to 0.5 mm. In such a case, a minimum print head-to-platen spacing of less than 0.2 mm would prevent proper operation of the printer and the user, in adjusting such spacing to accomodate various thicknesses of paper, must therefore be prevented from adjusting the spacing to less than that minimum amount. Thus, after such a "basic setting" has been effected by the manufacturer, the user cannot make this minimum spacing any smaller.
For example, in the Mannesmann-Tally printer model MT-140, the carriage guide shaft is guided in slide blocks which are disposed on the sideplates of the printer frame. To adjust the basic setting of the print head-to-platen spacing, the carriage guide shaft is relatively moved toward or away from the platen. With the basic setting adjustment completed, the carriage guide shaft is permanently bolted to the sideplates. This arrangement thus requires cumbersome, labor intensive and therefore expensive, and potentially inaccurate assembly and adjustment. In addition, the adjustment is prone to unintended change and, therefore, loss of the setting by loosening of the guide shaft securing bolts as a result of vibrations occurring during normal printer operation.